Regenerative reactors are conventionally used to execute cyclic, high temperature chemistry. Typically, regenerative reactor cycles are either symmetric (same chemistry or reaction in both directions) or asymmetric (chemistry or reaction changes with step in cycle). Symmetric cycles are typically used for relatively mild exothermic chemistry, examples being regenerative thermal oxidation (“RTO”) and autothermal reforming (“ATR”). Asymmetric cycles are typically used to execute endothermic chemistry, and the desired endothermic chemistry is paired with a different chemistry that is exothermic (typically combustion) to provide heat of reaction for the endothermic reaction. Examples of asymmetric cycles are Wulff cracking and Pressure Swing Reforming.
Conventional regenerative reactors deliver a stream of fuel, oxidant, or a supplemental amount of one of these reactants, directly to a location somewhere in the middle of the regenerative flow path of the reactor, without having that stream pass through regenerative beds or regions. By middle of the regenerative flow path of the reactor, we mean a region of the reverse flow reactor that is in between two regenerative beds or regions, with the main regenerative flow passing from one of these bodies to the other.
In most cases, this stream is introduced via nozzles, distributors, or burners that penetrate the reactor system using a means that is generally perpendicular to flow direction and usually through the reactor vessel side wall. For example, during the exothermic step in a conventional Wulff cracking furnace, air flows axially through the regenerative bodies, and fuel is introduced via nozzles that penetrate the side of the furnace, to combine with air (combusting and releasing heat) in an open zone between regenerative bodies. In a conventional symmetric RTO application, a burner is placed to provide supplemental combustion heat in a location in between two regenerative bodies. The burner combusts fuel from outside the reactor, either with the air passing through the regenerative bodies, or using external air.
Attempts have been made to introduce a reactant of the exothermic step to a location in the middle of the regenerative reactor via conduits that are positioned axially within one or more of the regenerative bodies. For example, Sederquist (U.S. Pat. No. 4,240,805) uses pipes that are positioned axially within the regenerative bed to carry oxidant (air) to locations near the middle of the regenerative flow path.
All of these systems suffer disadvantages. Positioning nozzles, distributors, or burners in the middle of the regenerative flow path of the reactor diminishes the durability of the reactor system. Nozzles, distributors, and burners all rely on carefully-dimensioned passages to regulate flow in a uniform manner, or to create the turbulence or mixing required to evenly distribute the heat that results from the exothermic reaction they support. By function in a regenerative reactor, these nozzles, distributors, are located at the highest-temperature part of the reactor. It is very difficult to fabricate and maintain carefully-dimensioned shapes for use at high temperatures. If the nozzles or distributor loses its carefully-dimensioned shape, it will no longer produce uniform flame temperatures.
A further disadvantage of using nozzles, distributors, or burners to introduce one or more reactant directly into the middle of the regenerative flow path of the reactor is that such an arrangement bypasses that reactant around the regenerative flow path, and thus eliminates the possibility of using the regenerative reactor system to preheat that reactant stream. The fundamental purpose of a regenerative reactor system is to execute reactions at high efficiency by recuperating product heat directly into feeds. Bypassing some fraction of the feed to the reactor around the regenerative system thus reduces the efficiency potential of the reactor system.
It is an object of the present invention to provide a means for operating a regenerative reactor system that alleviates these problems of the conventional design and operation of a regenerative reactor system.